1. Field of the Invention
The present invention relates to chillers and apparatus used for cooling loose food products or bagged food products. More specifically the present invention relates to chillers of considerable size which utilize water to cool a continuous food product flow.
2. Description of the Related Art
Chilling machines which utilize water to cool a continuous food product flow are well known. Food products are commonly moved through cylindrical cooling containers using helical conveyor screws. Products which are so moved through a container typically are gently pushed by the flights of the conveyor screw longitudinally through the lower portion of the container with little lateral movement. Thus if the container is partially filled with water for cooling the food product, the food product will often lie in relatively stable relation to the water with limited mixing. The heat exchange from the product to the water under such conditions is also limited, which in turn affects the capacity of the machine to cool the food product. Such limitation of the heat exchange rate has also limited the size and capacity of such machines, since larger machines will result in a greater mass of food product to be cooled by the cooling water, thereby creating additional efficiency problems. U.S. Pat. Nos. 3,097,501 and 3,410,101 illustrate such chillers in which animal carcasses are agitated by pressurized air blown into the apparatus, and in U.S. Pat. No. 3,410,101 axial rods at the flight perimeter and trailing lifting fingers provide further agitation. In U.S. Pat. No. 4,578,957, a packing plant by-products chiller is disclosed, having a long, inclined baffled rotating tank in which the by-products are cooled by a liquid coolant which is sprayed onto the by-product through spray nozzles on header lines. However, the tank contains no screw conveyor. Instead, the introduction of additional by-products and coolant, and gravity, pushes the previously introduced by-products through the tank.
Continuous chillers commonly require lengthy tank-like structures to sufficiently cool the food product being processed in the capacities required for commercial continuous food processing. The cooling process often takes as long as about 30 minutes to complete, despite improvements which have been made in the equipment. In many such chillers, cold water is added to the food product at several locations within the long tank. This often increases the quantities of water required for cooling, which may be both inefficient and increase plant waste water disposal problems. In particular, at the infeed end of many tanks, the temperature differential between the cold water and food product is particularly large since the food product is warm, while at the discharge end, the differential is particularly small because by the time the food product reaches the discharge end, it is fairly cool. It is known that counterflow cooling, wherein the cooling water traverses the cooling tank in a direction opposite to that of the product, maintains a more uniform temperature differential and better heat transfer between the product and the cooling water throughout the length of the tank. U.S. Pat. No. 3,426,546 to Crane discloses removing water at the discharge end of the chiller tank, cooling the water with ice and then adding varying amounts of the cooled water to the chiller at different locations along the length of the tank.
Despite the many variations of continuous cooling apparatus which have been employed in food processing, a need has continued for a continuous cooler which will cool a greater volume of product in less time and a shorter physical length of equipment and plant floor space, while attaining maximum efficient use of cooling water.